1. Field of the Invention
The present invention relates to an image information reading apparatus which can be used in a copying machine, a facsimile, a printer, etc., and which reads image information off an original sheet by utilizing at least transmitted light.
2. Description of the Related Art
An image information reading apparatus is known, as is used in a copying machine or the like, which comprises an original table. This apparatus has a scanner which includes a photoelectric conversion element. An exposure light beam is shone onto an original sheet placed on the original table, and is then either transmitted via or reflected by the original sheet. The photoelectric conversion elements converts this light beam into an electrical signal. The signal, i.e., a desired image signal, is supplied to a host computer or the like.
The apparatus further comprises a control circuit and a drive means of the conventional type. The control circuit controls the drive means. Under the control of the control circuit, the drive means moves the scanner back and forth along the surface of the original table, to scan the original sheet with a light beam.
Conventional information reading apparatuses may be classified into two types; those which read information off original sheets by means of reflected light, and those which do so by means of transmitted light.
Recently, an improved image information reading apparatus has been developed which can read information off original sheets by means of both reflected light and transmitted light. This apparatus comprises a housing, a glass plate mounted on the top of the housing, for supporting the original sheet, a scanner located within the housing, and a light source unit located above the glass plate. The scanner has a photoelectric conversion element and a light source for emitting light which is to be reflected by the original sheet placed on the glass plate. The light source unit has a light source for emitting light which is to be transmitted through the original sheet.
The scanner and the light source of the light source unit oppose, with the glass plate interposed between them. To read information off the original sheet by means of transmitted light, the light source of the light source unit must be moved in synchronism with the scanner, in the same direction at the same speed as the scanner. Hence, the apparatus requires two drive means, one for the scanner and the other for the light source of the light source unit, as well as a drive means for the scanner. Either drive means necessarily must includes a timing belt, a plurality of pulleys, a motor, a speed reducer, etc. Further, the apparatus requires a circuit for controlling both drive means, thereby to drive the scanner and the light source of the light source unit in synchronism. The apparatus is naturally more complex than the apparatus which reads information off an original sheet by means of reflected light or transmitted light. Particularly, the electrical circuit of the apparatus is complicated. It takes a long time to assemble the apparatus, inevitably raising the manufacture cost of the apparatus. Furthermore, the apparatus requires rather a high maintenance cost.